Now we're talking!!! (Uh... I just binged on orange)
Numero uno: Navel orange!!!!
But I luv'em all! The small ones (mandarin, tangerine) are very sweet can't eat many at once. Blood oranges have nice tartness but it's also not binge material IMHO.
Grapeftuits are somewhat fussy as u have to scrape out the flesh - i sometimes think I use more calories in doing so than I get from the fruit. 
Some time ago I bought a "Pommelo" which is the largest citrus ever. It's like a melon but in reality a grapefruit. At least the chunks of flesh u get out of it are huge - but it separates also much easier than normal grapefruit...
For pics look here:
http://www.foodsubs.com/Fruitcit.html
"I am an animal. Hath not an animal eyes? Hath not an animal hands, organs, dimensions, senses, affections, passions; fed with the same food, hurt with the same weapons, subject to the same diseases, healed by the same means, warmed and cooled by the same winter and summer as a human is? If you prick us do we not bleed? If you tickle us do we not laugh? If you poison us do we not die?"